Septic tanks could go up to 10 years between pumping if used properly.. .. SEPTIC TANK....the only things that should be going into it , is what has been processed thru you...I.E. sh*t and p*ss and the T.P.. ( pardon my french ) .......When garbage disposers put in ground up food that needs to Decompose............ anti- bacterial hand soap the kills the living bacteria........kitchen grease that coat the top layer of the drain field that stops the water from seeping back into the ground........Too much hair shampoo...... toilet bowl cleaners........no feminine products.........ALL BAD........ ............. You just need to add baking yeast a few times a year.......It appears that the lines from the house to the tank would be a place to start, too much blockage to keep the ( only ) three previously mentioned items flowing freely....................The stack vent could be blocked with some thing ..I.E. birds nest, bats, that is stopping the air movement during the flushing/water flow and the venting of septic gas....

After the septic is pumped out, and ask the guy if the system is suited to the family size and water usage. Then, I would have a real plumber evaluate the home plumbing system and perform the needed modifications and maintainence. Use a company that can run a camera through the lines to check them out. The newer process of "water-jetting" the drain lines instead of just snaking them will clean out the entire inside of the pipes.

Also you might want to try to take steps to reduce the ammount of water you are putting into the system. You might just be putting out more than the leach field can take. A High Efficiency washer would help if you are using a standard washer. So would flow restriction facuets and shower heads. If you toilets are old, 3 gallon flush, replace them with 1.6 gal flush models.

" Giving numerical data to Sears management is like giving a monkey a machine gun. No one knows for certain what will happen, but you can be sure of two things... It will be real messy, and only the monkey will be unharmed"